Sulphur-nitrogen relationships in the tropical legume Stylosanthes humilis

Abstract

The effects of age and sulphur fertilization on various sulphur fractions in the legume Stylosanthes humilis were examined. Plant material was obtained in two consecutive seasons from nodulated plants growing in the field and from a glasshouse experiment. A very close relationship between the concentration of total nitrogen (Nt), that of total sulphur (St), and age was found. In young material Nt increased at first then reached a plateau with increases in St (brought about by additions of sulphur). As the plants aged, however, both Nt and St declined and the relation between them became more nearly linear. Nt and St were also closely related in seed from these plants but the St/Nt ratio was much lower than in the vegetative material. A moderate deficiency of sulphur had little effect on the ratio of alcohol-insoluble to total nitrogen. In contrast with published work on other species it was found that sulphur applications increased the ratio of sulphur to nitrogen in the alcohol-insoluble (protein) fraction.

Indexes of Sulfur Deficiency in Alfalfa. II. Plant Analyses1

“…The leaf/stem ratio has also been observed to increase in S-deficient alfalfa (14). This would cause a further increase in the (N/S)p ratio of whole plants and may help explain our results and those reported by others (6,9,15). In contrast, data reviewed by Dijkshoorn and Van Wijk (4) showed that the concentration of cytoplasmic proteins decreased faster than that of the chloroplastic proteins, thereby causing a decrease in the (N/S)p ratio in S-deficient barley leaves.…”

“…4 This ratio increased from about 17 to 18 at adequate S levels to near .23 under S deficiency. An increase in the (N/S)p ratio with increasing severity of S deficiency has also been observed in studies with barley (Hordeum distichutn L.) (6), white clover (Trifolium repens L.) and ryegrass (Lotium perenne L.) (15), and a tropical legume (Stylosanthes humitis L.) (9). Other studies indicate that the (N/S)p ratio is a constant, near 17.5 for Leguminoseae (4, 19).…”

“…(11), and sugarbeets (Beta vulgaris L.) (10) have also been reported. However, not all studies are in agreement (2, 18,22), and recently the constancy of the (N/S)p ratio has been questioned (9,15).…”

Mineral constraints to nitrogen fixation

“…However, in cases where the nutrient affects nitrogen metabolism rather than nitrogen fixation, there is a decrease in protein nitrogen under deficiency as in the case of severe S deficiency (Anderson and Spencer, 1950b;Andrew et al, 1952). In contrast, mild S deficiency may limit nitrogen fixation directly since there is little or no change in the ratio of protein nitrogen to total nitrogen (Gates et al, 1966;Jones et al, 1971;Walker and Adams, 1958).…”

“…Specific involvement has been claimed in cases where nutrient applications increase both legume growth and nitrogen concentrations in plant tops. Examples of increases in nitrogen concentrations of symbiotic legumes following correction of nutrient deficiencies have been reported for Ca in T. subterraneum (Banath et al,, 1966;Loneragan, 1959); Co in Lupinus angustifolius (Chatel et al, 1978); Cu in T. subterraneum (Greenwood and Hallsworth, 1960;Snowball et al, 1980) and T. repens (Van der Elst et al, 1961); Mo in T. subterraneum (Anderson and Spencer, 1950a) and in Macroptilium atropurpureum, Glyeine wightii, Desmodium intortum and Lotononis bainesii (Johansen et al, 1977); P in T. subterraneum (McLachlan and Norman, 1961) and Stylosanthes humilis (Gates and Wilson, 1974); S in T. subterraneum (Anderson and Spencer, 1950b), D. intortum and L. bainesii (Andrew, 1977b), and S. humilis (Jones et al, 1971) and Zn in M. sativa (Lo and Reisenauer, 1968). However, such results should be interpreted with caution since increases in plant nitrogen concentrations may also reflect changes in plant structure (e.g.…”